A conventional loudspeaker, or “speaker”, as used herein, may use a moveable diaphragm, or “speaker cone” to produce sound. Some speaker cones have radially symmetrical curvature, but may have shape variations (some are almost flat) that vary the geometry of the diaphragm from a strict geometric cone. The speaker cone is moved by a former, which also supports the voice coil. The former is attached to the speaker cone. The voice coil, which rests in the magnetic field of a magnet assembly, receives an audio-encoded electrical signal, or “audio signal”, which causes varying current in the voice coil. By interaction of the voice coil current with the magnetic field of the magnet assembly, sound-producing movement of the former and speaker cone results. The voice coil is constrained to one-dimensional motion, perpendicular to the base plane of the speaker cone, by a flexible support structure called a “spider.” The magnet assembly may comprise a magnetically permeable pole piece, a permanent magnet, and a magnetically permeable top plate. The pole piece may feature an annular groove, or “air gap,” to permit motion of the voice coil deeper into the magnetic field of the magnet assembly. The speaker cone is supported at its widest perimeter by a flexible suspension, or “surround”, which, in turn, is supported by a structure called a “basket.” The top plate of the magnet assembly and the spider are also connected to the basket. An opening in the speaker cone at its center may be covered with a dust cap, which reduces the amount of dust that may affect voice coil motion in the annular groove. At least a portion of the surround conventionally has a semi-circular or sinusoidal transverse cross-section.
Shallow speakers, as the term is commercially used, are speakers with reduced depths. The depth of a speaker is the maximum dimension of the speaker parallel to the longitudinal axis of motion of the speaker. The advantage of a shallow speaker is that it may be used in mounting environments where thicker speakers may not be suitable. For example, shallow speakers may be used in conjunction with flat screen television sets, automobiles, or audio systems for small apartments. The reduced depth of shallow speakers can come at the cost of reduced excursion for the diaphragm.
The amount of sound produced by a speaker is proportional to the air volume displaced by the diaphragm in its axially oscillatory motion. The volume displacement, in turn, is determined as a function of the area of the plane of the diaphragm at its largest point and by the maximum distance it can travel from a quiescent state, called the speaker's “excursion.” The designer must strike a balance between the size of the excursion, enabling more sound if the excursion is larger, and the depth of the speaker. Accordingly, the aim of shallow speaker design is to find ways to maximize volume displacement while maintaining high sound quality and minimizing depth.
Significant problems arise from the use of glue in the manufacture of speakers. The glue joints age faster than other connections. The aging takes the form of strain hardening and stress fracture in the glue joint, resulting in failure of the speaker. Some glue joints are riskier than others. High-risk glue joints are glue joints that connect two rigid members in contact in a moving system, or connect more than two members, whether rigid or flexible.
The cost of manufacture is another important consideration in speaker design. Intricate manufacture means expensive manufacture, quality risks, and reliability risks. Generally, designs having many parts or features will require more intricacy in manufacture than designs having fewer parts. The number of attachments that must be made between the parts is also a contributor to manufacturing cost. Alignment is also part of the manufacturing problem. The more separate pieces that have to be aligned about the longitudinal axis of speaker motion, the more difficult and expensive the manufacturing of the speaker becomes.
There have been attempts by others to accomplish shallow speakers without sacrifice of excursion. Proni (U.S. Pat. Nos. 5,734,132, 6,095,280, and 6,501,844) employs a substantially cylindrical tubular suspension, of greater diameter than the magnet assembly, attached between a spider and a diaphragm. Proni's approach requires intricate manufacture and high-risk glue joints. Proni does not provide vents in the tubular suspension itself, but provides an optional ring (which you really need!) between the diaphragm and the tubular suspension, which provides vents. Proni also teaches rigid-to-rigid glue joints.
Funahashi (U.S. Pat. Nos. 7,203,333, 7,209,570, and published U.S. patent applications 20060215871, 20060245615, 20070177757) adopted a principle of operation of reducing the effect of non-linearity in the surround by using an inverted second edge, or surround, for the rear suspension, in place of a spider. Funahashi's approach requires intricate manufacture and high-risk glue joints. Funahashi's second edges require more clearance than spiders, and the stiffness is not progressive, as with a spider. Funahashi's use of the inverted surround requires a suspension holder between the second edge and the bobbin, or former, to reach across the space that a longer spider would otherwise occupy, and to avoid the magnet assembly. Funahashi's diaphragm and suspension holder are rigid and are glued to the rigid bobbin and, in some embodiments, to each other. Funahashi's approach requires a glue joint between the second edge and the rigid suspension holder, and limits the damping action to the frequencies affected by the edges. Funahashi uses the rigid inner portion of his suspension holder to support the diaphragm in a triangular structure with the bobbin that apparently attempts to compensate for the propensity of second edges to flop about, rather than firmly center the bobbin and voice coil. Funahashi's last U.S. application indicates that the success anticipated for his earlier work did not fully materialize.
Sahyoun (U.S. Pat. Nos. 7,185,735, 7,197,154, 7,225,895 and U.S. Patent published application 20040076309) also adopted a principle of operation of reducing the effect of non-linearity in the surround by using an inverted second edge, or surround, for the rear suspension, in place of a spider. Sahyoun's speakers also require intricate manufacture and high-risk glue joints. Sahyoun's outer V-shaped diaphragm flange has two surrounds attached. Sahyoun's second edge also limits the damping action to the frequencies affected by the edges. Sahyoun also teaches a spider glued to an apex of a V-shaped diaphragm optionally with an additional diaphragm overlaying and glued to the V-shaped diaphragm. Yet another embodiment of Sahyoun teaches a vertically downward flange of a diaphragm.
Kreitmeir (Published U.S. Patent Application 20040165764) also teaches inverted opposed edges for improving linearity as well as a support structure to improve the rigid joint created by the diaphragm and the bead mount between the bobbin and the inner edge. Kreitmeier's speakers also require intricate manufacture and high-risk glue joints, as well as additional power to move the mass of the support structure.
Horigome (Published U.S. Patent Application 20070127768) also teaches inverted opposed edges for improving linearity. Horigome teaches a rigid drive cone glued between the inner edge and the rigid bobbin, with the rigid dust cap and the rigid diaphragm glued to an apex of the rigid drive cone. Horigome forms a gas-tight space with his drive cone, frame, edges and diaphragm to create an air spring. Horigome's speakers require intricate manufacture and very-high-risk glue joints, especially at the juncture of the cone, dust cap, and diaphragm.
Kato (U.S. Pat. No. 6,672,423) teaches an inverted rigid V-shaped cone glued between the rigid bobbin and two parallel spiders with the rigid diaphragm connected to the inverted V-shaped cone at the apex. A cone paper extends from the surround to attach to the forward spider. Kato's speakers require intricate manufacture and high-risk glue joints.
Kobayashi (Published US Patent Application 20050141746) also teaches inverted opposed edges for improving linearity. Kobayashi teaches a rigid drive cone glued between the inner edge and the rigid bobbin, with the rigid dust cap and the rigid diaphragm glued to an apex of the rigid drive cone. Kobayashi forms a gas-tight space with his drive cone, frame, edges, and diaphragm to create an air spring. Kobayashi's speakers require intricate manufacture and very-high-risk glue joints, especially at the juncture of the cone, dust cap, and diaphragm.
Watanabe (Published U.S. Patent Applications 20050276435, 20060018500, and 20060120554) teaches a rigid stepped cylindrical connection member attached to two parallel spiders. Watanabe's rigid connection member is incredibly intricate to manufacture, some versions appearing all but impossible to die press. Watanabe uses rigid metallic terminal members secured in recesses in the sides of the connection member to conduct the audio signal from a tinsel to the voice coil leads. The rigid connection member is glued to the underside of the rigid diaphragm, in the vicinity of the front end of the voice coil bobbin, by a circumferential bead of glue. Watanabe's speakers require extremely intricate manufacture and very-high-risk glue joints, especially at the juncture of the connecting member and diaphragm.
The inventors have recognized a need for a shallow speaker that is simple to manufacture that suffers no sacrifice of excursion, power, and no loss of sound quality. The inventors have also recognized a need for a fully integrated new design for a shallow speaker. The inventors have also recognized the advantage of minimizing the number of glue joints in the design, especially high-risk glue joints. In order to meet those needs, and to solve related problems, the inventors have developed the novel shallow speaker of the present invention.